US1564566A - Art of drying materials - Google Patents

Description

Dec. 8, 1925 G. D. HARRIS ART OF DRYING MATERIALS Filed Feb. 18. 1924 s sheets-snee; 2

Dec/8, 1925. 1,564,566

G. D. HARRIS 1 ART. OF DRYING MATERIALS Filed Feb. is, 1924 6 s sheetssheet I ,4 TroR/VEY.,

Patented Dec. 8, 1925. fr

"UNITED STATES PATENT OFFICE.-

GORDON DON' HARRIS, OE FREEPORT, NEW YORK,` ASSIGNOR TO THE INDUSTRIAL DRYER CORPORATION, STANFORD, CONNECTICUT, vA CORPORATION F CON- NECTICUT.

ART OF DRYING MATERIALS.

t j To all 'whom zt may concern.'

Be it known that I, `GronnoN DoN HARRIS,

'l a citizen of the United States, residing at Freeport, county of Nassau, and State of' New York, have invented a certain new and useful Improvement in the Art lof Drying Materials, of which the following is a specification. f

This invention pertains to the art of dr ing materials in accordance with a determined or prescribed formula with respect to the conditions of temperature and humidit ture and the moisture content of such dryof the drying atmosphere and also wit 1 reference to the moisture coutent and the character ofthe material under treatment.

' The invention includes both a method and an apparatus, and it is used for the treatlnent of a wide variety of materials, including leather, ceramic Ware, and other products the physical characteristics of which demand that during the drying period there shall be present in the drying atmosphere flowing into contact with the material the requiredheat units to eect the exchange of heat in ,theatmosphere for .moisture in the material and that such drying atmosphere shall contain, also, a certain humidity the percentage of which is in a definite ratio to the moisture content of the material under treatment.

ln 'the treatment of a certain class of materials, such as leather, it has ,been determined by experience and investigation that, to attain the required results in conditionmg such material, the drying atmosphere' shall be maintained at a constant temperaing atmosphere, shall, also,

be constant, irrespective of a decrease 1n the ratio of moisture diffusion within the material under4 treatment, to the end that the heat carried 'by the drying atmosphere will be exchanged for moisture in the material While the lmmidity pesent in the drying atmosphere will also carried into contact with the material with the object rof precluding that condition of such material known` as case hardemng", wherein a film on the surface closes the pores against the free "exudation of moisture present Within the mass of such material.

Again, in the treatment vof other classes of materials, such as ceramic wares, it has been determined -byinvestgation and expetl'le interior of moisture decreases from the material under` treatment, the heat units and the percentage of moisture present in the drying atmos- ,phere shall vary as the drying of the material progresses, with the result that the heat i units present in the atmospherewill progressively increase and the moisture content of the atmosphere will also progressively increase, or vice versa, the atmosphere will carry heat units in decreasing percentage while the moisture content of such atmosphere will remain constant, or be increased. As an example, in the condi-tion vof the drying atmosphere, for evaporating materials such as leather, wherein constant temperature and constant humidity are desirable, the drying atmosphere is heated to a temperature of 100 Fahr., and` contains 85 humidity, and these conditions of heat and humidity are rendered constant by boosting the atmosphere and renewing such atmosphere at a more or less frequent interval, determined and controlled by the condition of the atmosphere itself acting through instrumentalities known to the art, whereby an excess of humidity in the atmosphere sets into action certain mechanism that auto evaporation progresses, to the end that the evaporation from the material shall be carried on under conditions which preclude fractures in and breaking of the material itself. Experience in .the treatment of ceramic materials to elimirate moisture there'- from preparatory to firing or bakin the materials in order to vitrify the same, s qws 'that a large percentage of breakage 1s 1ncurred due to the un ual or ununifqrm evaporation of moisture om areas varying product under treatl' les there is present in each piece of material, such as ceramic ware, certain parts of greater cross section than other parts of such materal which are comparatively thin in cross section, andwhile the dryingof the areas of thin cross section is not diliicult of accomplishment, the problem is presented of -evapor-ating moisture from the areas of thicker cross section in a definite relation to the evaporation taking place in areas of thin cross section, because the fractures of the material are -occasioned by the une ual contraction and expansion of the ma erial itself in the process of eliminating moisture from the areas of thin and thick cross sec-` tions. According to my invention,-vthe drying atmosphere itself is nditioned both as concerns the heat carrigd thereby, and as to its moisture content, and such conditioning of the atmosphere is controllable automatically, to the end that the heat and the humidity shall vary as the evaporation of the materials progresses, such variation including an increase of heat units and an increase in the moisture content of the drying atmosphere. At the initial stage in evaporating moisture from ceramic ware, the drying atmosphere is conditioned by heating it to a temperature of 75 Fahr. and charging or supplying moisture to-95" humidity, but

as the evaporation of moisture proceeds from the ceramic ware, it is found that the areas of thin cross section will become dry, or relativelydry, whereas the areas of greater cross section will still contain an appreciable mois ture content which it is essential shall be eliminated during the drying process without resulting in fracture' of the ware itself and which elimination of moisture shall be effected prior to ring or baking-the ware.

- Accordingly, as th dryingprogresses the drying atmosphere is conditioned according to the formula or specification by increasing the heat" units and by increasing the moisture content Npresent in such atmosphere, to the en dv that the,heat units of the atmosphere will be exchanged for' moisture in the areas of. thicker cross section of the ceramic ware, Whereas the humidity of\ the'atmos phere will so act upon the areas of thin cross section of such ceramic ware as to supply noisture to such thinner areas from the atmosphere itself, as a result of which the ceramic ware is itself conditioned by the drying atmosphere to the end that unequal expansion and contraction of the ceramic ware, and the yattendant fracture thereof, is

eliminated or minimized, but on the other hand, the evaporationof moisture from vsuch ceramic ware proceeds gradually and steadily in all areasthereof, notwithstanding the vvariationin thev cross sectional areas, and

without entailing the breakage so prevalent in the older methods of drying materials ot v Figure 3 is a vertical -mosphere, the latter bein this character. As inthe example hereinbefore mentioned in connection with the evaporation of materials such as leather, the drying atmosphere for treating material such as ceramic ware, is conditioned by heating and reheating such atmosphere to the required temperature or temperatures, and by renewing a definite volume of moisture laden atmosphere with a similar volume of fresh atmospheric air, such conditions of said atmosphere setting into action the tempera ture and humidity controls whereby the acts of boosting the atmosphere and of renewing the same with fresh atmospheric air are performed automatically, and in case the moisture. content of the a/cmosphere is or becomes too low to conform to the formula or specifications, certain controls act to supply humidity tothe atmosphere by feeding thereto a definite volume of live steam from an available source of supvconstantl the humidity of the atmosphere, or

for increasing the moisture content, and provision is made, also, for vincreasing' the moisture content of such atmosphere by feeding moisture thereto, all such controls being effected to conform with more or less accuracy tothe prescribed formula or standard, andto attain such ends usually by automatic mechanism.

Other functions and advantages of the invention will appear from the following description taken in connection with the drawings, wherein Figure 1 is a vertical section of a drying apparatus suitable for carrying into practice my invention, and

Figure 2 is a diagrammatic view illustrating oneform of controls by which the atmosregards its temperature and humidity and irrespective of the ratio of diffusion of the I water content present in the material under treatment. A

sectional elevation illustrating another arrangement of the air intake and the air outlet with respect to the blower and to other parts of the apparatus.

A is a chamber within which the material to be treated is positioned in a manner to be exposed to the action of a drying atrecirculated by the rotative motion of a an or blower B. AsI shown, the chamber is provided with perforated floor a and a perforated roof a', the saine being adjacent the bottom and the top, respectively, of the exterior casing so as to produce an intake flue A and an eduction flue A2 which are in communication with the chamber through the perforations in Isaid. floor g and the roof a', respectively.

V'the intake flue A At one end of the apparatus is a heater chamber C connected at the bottom with and at the top with a feeding duct D, and within said heater -chamber is asuitable heater or radiator E, the same being shown as-a steam coil ,with a header e, to' which is connected a steam .supply pipe F leading from a source of steam supply, see Figure 2.

The circulating mechanism B for the drying atmosphere 1s operatively positioned in the feeding duct D, and said circulating mechanism is driven by power of any appropriate kind", so as to drive the blower at the required speed.

" The feeding duct is connected. at ,one end through a port al to the eduction flue A2 of d the material. chamber, whereas the other end of said feeding duct is in free communication with the heater chamber` C. To

this feeding duct is coupled an intake duct G open to the atmosphereV and operable under certain damper controlled conditions for lfeeding fresh `atmospheric air to the feeding duct and thence through the heater chamber C to the material chamber A.

A discharge duct H is connected tothe feeding duct D, the same being at an appreciable distance from the fresh air intake G and the two ducts beineIr wholly independent of each other, although both of them are in communication with the feeding duct. In the fresh air intake is positioned a valve or damper g, whereas a similar valve or damper k is mounted in the discharge duct H. Said dampers g, la, are'hung. for pivotal movement within the respective ducts G H, and as shown', the dampers are conjointly. operated by a` rod llinked to th'edampers so as to open dampers whereby the fresh air duct G is Vopened and closed concurrently with the openingand closing of the moisture laden air discharge duct H., With the dam ers g, ft, in closed positions lwithin the uets G H. and with the blower in motion, said lblower draws the drying atmosphere from chamber A through the duct D and blows the atmosphere through chamber C and thence into the chamber A, the effect `offwhich is to recirculate the atmosphere alternately through chambersY A C and thus to reheat and boost the atmosphere by 'contactwith the radiator E. By opening the dampers 'r/ h, in the lues- G H, respectively, and4 an outlet 1s prowith the blower inzmotio'n, vided through duct H forl discharging moist hot air Vin a definite volume, and at the same time the'blower draws in a corresponding volume of fresh atmospheric (new) 'air to replace the moist air thus discharged from the circulatory path, which latter includes chambers A C and duct D. The' fresh air thus drawn into the circulatory path byand1 close the i thermometer the blower is mixedfwitli the warm,

moist air and thus the drying atmosphere is conditioned by the admixture therewith of new air and by boosting the same through the action of the radiator E.

The flow of steam to the radiator is controlled by a valve I, and this valve is in 'turn under the control of an automatic temperatureregulator J responsiveto the temperature of the drying atmosphere and positioned within chamber A, said temperature regulator being of `any character suitable for the purpose and adapted to be .set

manually, so that upon Va decrease in thethe drawings there is shown a fluidpressure j mechanism which is operatively related not only to the temperature regulator, but is 'similarly' related to the humidity controls, presently referred to. The motive fluid (air in the example shown) is accumulated withi in a tank K by theaction of a compressor 7c driven by a motor le', said compressor having a valved connection 7a2 -with said tank, and from this tank leads a main l, from which is branched a plurality of ipes m, 71,( o. The pipe in. is connected wit temperature regulator J and leads thence through a branch mto automatic valve I, whereby` the action of sa1d regulator J, responsive v. `to a change in the tem ing atmosphere, contro' elf the ow of steam tothe radiator, as the mosphere may demand.

erature of thedry- -the flow'. ofaimo- 'tive iuifd to the valve I vfor automatically said valve inv feeding and shutting An excess.. of humidity in-'the .dryingatmosphere, i. e. an increase in the moisture content of sa1datmosphere above that conditionl whlh 1t 1s desired to establ1sh and maintain in said atmosphere, influences -a control mechanism P which v1s responsive to 'an lncrease or decrease 1n the moisture content ofthe drying atmosphere, and which is positioned within chamber A so as to be' ex-v posed for Contact with the atmosphere circulating into contact with tlie'material. 'Said humidity control mechanism P includes a wet bulb thermometer p' and .a dry bulb pf with a well known'provision for manually setting said therm meters in amanner toinsurethe action of Ale control mechanism as a unit when the moisture content ofthe drying atmosphere exceeds ther limit of the humidity desired. Said humidity responsive control mechanism P is operatively connected with a damper shifting mechanism herein illustrated in the form oi a pistoucylinder N within which is slidable a spring-actuated piston N the -rod of which is connected to a bell crank q linked by a'rod g to another bell crank g2, the latter-being pivoted to thedamper 4rod z', see Figure 2. With the humidity control mechanism P co-operates the motive fluid 'pipe n: .leading from .the lmain Z, said pipe n having a branch leading from the thermometers p p to and connected with, the damper actuating mechanism. The humidity responsive control P is manually set to become operative when an excess of humidity exists' in the drying atmosphere above that limit at which it is desired to maintain said'atmosphere, and when this condition is reached,

the elements p p open the path for the flow 4 of motive fluid through pipes n n to the pistonmechanism, whereby the dam ers g,

h, are opened automatically for the lower to draw in through the intake duct G a supply of fresh atmospheric (new) air, and at the same time to expel through the discharge duct H a corresponding Volume o humid hot air. Provision is thus made for conditioning the drying atmosphere by expelling a definite volume of humid air and replacing the expelled air with fresh air, whereupon the control mechanism P is influenced to shut yofthe 'flow of motive fluid to piston cylinder N and the dempers g, h, are closed in the intake and exhaust ducts G H, respectively.

f Provision is made for automatically feeding moisture into. the drying atmosphere should the humidity all below a determined limit, experience having shown that there are occasions in the service of the machine when the drying atmosphere attains a low' humid condition unsuitable for the treatment of a material or materials possessing certain physical properties, as, e. g. in the 'evaporation of moisture from ceramic ware of ununiform cross sectional dimensions and4 in the treatmei t of hides the cross sectional thickness of which varies in different areas. v

A steam jet nozzle R is positioned for dischargin live steam into the feeding duct D for a mixture with the drying atmosphere mi the`dry1ng atmosphere.

mechanism S is a thermometer of a known, type, positioned inchamber A for exposure yto be recirculated by the blower B, and to this jet nozzle is coupled, a feed pipe r branchedol' the steam main F. The 4iow of steam is established by opening an autoy lnatic valve R inth'e pipe 7', and this val/ve i's actuatedautomatically by a control mechanism S responsive to a 10W moisture 1content- Said control to Contact with thedrying atmosphere, andr @5 provided `with setting mea-ns operable. manually to render the thermometer responsivey to the moisture content of the atmospherev4 when it decreases below a desired llmlt.

With this control mechanism Sco-operates the motiveii-uid pipe 0 having a branch o leading from the control element S to the automatic valve whereby said valve is actuated by the vmotive lluid supplied by y,

pipe o when the control element S is 1nluenced by low humidity of the drying atmosphere. A

In operation, the material to be treated 1s placed within the chamber A, steam admitted tothe radiator, valves g, h, closed, and fan Bu set in motion for circulating air within the closed path afforded by chambers A, C and duct D. The-air is heated to the required temperature by radiator E, and the iiow of air into contact with the material effects the exchange of heat for moisture, so that the temperature of the atmosphere will be decreased by such exchange, although the reheating or boostingof such atmosphere during its'repeated circulation compensates for the loss of heat units due to such exchange. and humidity controlsexposed to the drys ing atmosphere, it follows that the steam supply is cut oli' from the radiator when the temperature of the atmosphere remains constant, and with the moisture'content of the atmosphere at the desired saturation, the dampers g, l1., are closed, thus effecting the recirculation by the blower of the atmosphere withinthe closed path. Where a con- With the temperatureO stant determined humidity and temperature of the drying atmosphere are desired for treatment of the material"`within chamber A, say at 100g Fahr. and 85 percent humidvity, the thermometer control J and humidity control P will influence the radiator E and damper shifting mechanism N N" g g g2,

sol as to supply steam' to the radiator 4 either one-or all of'them, take .place whenever the` .condition ofthe drying atmosphere changes to such an extent that the tempera-` ture and humidity of 'such atmosphere are not, in accordance with the formula or specification determined as desirable for the treatmentl offa particular material. Obviousl ,the y increase in the moisture contentI of t e atmos here is dueto moisture evaporated ,from tie product,` whereas the temperature changes ared'ue to 'absorption by such atmosphere of the 'moisture which is exchanged for heat, suchchanges in the condition of' the drying atmosphere taking 1n la definite ratio to evaporation, to maintain the desired operating .temperature of the drying atmosphere.

Again, the humidity control P with the damper shifting mechanism act to open and close the dampers g, h, when the drying atmosphere reaches a certain moisture content, whereby the valves are opened for exhausting a definite volume of overcharged humid atmosphere, and to renew the atmos here by the admission of a proper volume'o new air which is mixed with the moist humid atmosphere remaining in the apparatus, so that the drying atmosphere is conditioned in conformity with lthe formula or specica- 'tion determined upon as suitable or most desirable for the treatment of a particular product. Furthermore, a decrease in the humidity of the drying atmosphere,as happens in the treatment of certain products, although the temperature may remain constant, or even increase as the evaporation progresses, such decrease affects the low humidity control AS vso as to actuate the valve R' and provide for the flow of steam to the nozzleRfin order to supply moisture to the drying atmosphere until such atmosphere attains the desired moisture content,

whereupon the-control S closes the valve R- and shutso the continued supply of steam to the nozzle.` In treating materials, such 'as ceramic ware, with or by a drying atmosphere the temperature and humidity of` which will bev'ari'ed as the drying progresses in conformity with a determined 'formula or f "specification, the drying atmosphere initially is, say, at 75 Fahr. and 95 per cent humidity, but atdifferent stages 1n the rogress of the evaporation of moisture from t e `product, the atmosphereis conditioned to varyl1 the temperature or the humidity,- or bot temperature and humidity are varied inconformity with the formula thi-ou h the action of the controls J, P, S, anti their associated devices,- either independently or conjointly,

*in a'manner to su ply`steam to the-radia- .torttoo eii the p ampers 'for the exit of humid atmos here and, for the in s of new air, and. or the addition of moisture to 'the drying. atmosphere to-be recirculated -within the-closed' path, whereby the drying yatmosphere is itself conditioned .both as respects thetemperature and moisture con-v ten either as to excess or decreased humidity, so as to, attain varyingv degrees in the temperature and humidity of thel atmos, phere, and to utilize suchconditioned atmospherein such manner-as to constantly maintain a proper condiion ofthe product under-1' going the drying and conditioning'treat--l ment. f

v In the apparatus shown in Figures 1 and p y 2, the air intake G and air outlet H are ositioned atI one side of blower B, i. era ja. cent the suction sideof said blower. It

may beadvantageous to position the outlet r H adjacent the pressure side of the blower, and in Figure 3 there is illustrated another `form of apparatus, wherein the blower B is positioned intermediate the ends of flue D, the outlet H for the dr ing atmosphere is connected with iiue D a jacent the pressure side of the blower, whereas the air inunderstood that the purpose is to locate the blower intermediate the air intake Gand the air outlet H.

aving thus fully described the invention, what I claim as new and ldesire to secure by Letters Patent is:

1; In the art of drying and conditioning materials, ,the process which consists in re@ circulating a drying atmosphere within a determined circulatory ath closed against the admission of \outsi e atmospheric air, heating the drying atmosphere during its recirculation, conditioning the drying atmosphere by the admixture of fresh atmospheric air therewith and Vby discharging from the circulatory patha definite volume of the atmosphere surcharged with moisture, and controlling the reheating and the renewal of such atmosphere, such vcontrol bein depend-'I ent upon and responsive` to a ciange or changes in the condition of the recirculated atmosphere itself. l

2. In thefart of drying and conditioning materials, the process which consists in re` v circulating a drying atmosphere within a definitel ath lclosed against the admission of outsi e atmospheric air, repeatedly heatingl such atmosphere during its recirculation, conditioning the recirculated vatmosphere by discharging from the circulatory path a definite volume of the atmosphere surcliarged with moisture and replacing the atmosphere so discharged with fresh atmospheric. air, and controlling the reheating and the 'conditioning of the recirculated at mosphere at stagesdependentt upon and responsive'to changes in the temperature and moisture content'v lof the atmosphere' itself. e

3.- In the l rtfof drying and vconditioning materials, -.t e` process which consists in reat stages dependent upon and res onsive to during its recirculation, periodically con-Y of the atmosphere dependent upon changes in the moisture content of lthe atmosphere itself. v

5.' In the' art of drying and conditioning materials, the process which consists in recirculating a drying atmosphere within a determined circulatory ath; periodically reheating the circulate atmosphere, controlling the periodsl of such reheating by a decrease in the temperature of the atmosphere ditioning the atmosphere during its recirculation by dischargin a. definite volume from the circulatory patV and replacing with fresh airfthe volume so discharged, and controlling the periods of such reconditioning of the atmps here at stages indicated by the presence o a moisture content in excess of aj determined percentage of humidity in suchatmosphere. p

6. In the art of drying and conditioning materials'the cross sectional areas of AWhich vary in thickness, the process which consists in recirculating a drying atmosphere characterized -by the presence of a definite moisture and heat content into contact with said material, exchangingp heat from the drying atmosphere for moisture in the material at continuous stages in the recirculation of the atmosphere, and at certain stages in the conditioning of ,said niaterial feedingmoisture to the areas of thmner cross section and concurrently therewith eva orating. moisture fromkthe areas of tliic er cross section, whereby the conditioning of the material areasvarying in cross sectionwill progress in definite ratio.

7. Iii the art of drying and conditioningl materials the cross sectional areas of which vary in thickness, the process which consists in recirculating a drying atmosphere `char.

acterized by a definite irioitiire and heat content intocontact with, said material for exchanging heat for moisture and ultimatelyy attain the supply 'of moisture to the areas of thinl cross section While continuing to evaporate moisture from the areas of thicker A cross section, reheating said atmosphere durji/ng Ythe v.recirculation thereoffto maintain its Maanen temperature constant, conditioning said atmosphere by discharging a definite volume of humid atmosphere and feeding th'ereto a like volume of fresh atmospheric air, and controlling the periods of such reheating and 'such conditioning of the atmosphere at stages which indicate-a change in the temperature and moisture contentI 'of such vatmosphere. e

8. In the art of drying and lconditioning materials, the process which consists in recirculating a drying atmosphere characterized by a definite heat and moisture content into contact with the material under treat ment, reheatin said atmosphere during the recirculation t ereof, conditioning the atmosphere during recirculation by replacing a 'definite volume of humid atmosphere with a similar vvolume of fresh atmospheric air, and controlling such periods of relieating and conditioning of the atmosphere upon a change in the temperature and in the humidity of such atmosphere indicating a drop below a determined limit of heat and moisture content of the atmosphere.

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9. In the art of drying and conditioning ized by a determined heat and moisture conl u tent into contact with the material, conditioning the atmosphere during recirculation by replacing with fresh atmospheric air a definite volume of such atmospheric air containing an excess of moisture, reheating the atmospheric air during recirculation, and

feeding steam into the `atmosphere during recirculation to bringthe moisture content to a desired limit 'or limits,

11. In an apparatus for drying and conditioning materials, means for Dcirculating a drying atmosphere within a circulatory path ,closed to the admission of outsidev atmospheric air, means for reheating such atmosing means, and humidity responsive meansv for controlling means operable for ,conditioning the atmosphere, by replacing a 'deiiiiteyoluine-o humid atmosphere with a like'volume of fresh atmospheric air.

12. -In an apparatus for dryingand conditioningl materials, lmeans for. circulating a drying atmosphere withinla circulatory,

llO

- drying atmosphere said atmosphere,

i y path closed tov the admission of outside at- Amospherio a1r, meansfor reheatmg such atf mosphere, means for conditioning the atmosphere by replacing a definite volume of humid atmosphere with a' similarvolume of fresh atmospheric air, and humidity-responsive'means exposed to thecir'culating atmosphere and operatively related to said conditioning means to actuate the latter upon a change in the moisture content of the atmosphere.

13. In an apparatus for drying and conditioning materials, means for circulating a drying atmosphere Within a circulatory path closed to the admission of outside atmospheric air, means for reheating such atmosphere,.means including a damper controlled exhaust and a damper controlled intake for replacing a definite volume of humid atmosphere with a like volume of fresh atmospheric air, and humidity responsive means positioned for contact with the atmosphere and operatively related to said exhaust and intake for shifting the dampers automatically upon an increase above a determined 11m1t 1n the moisture content of' said atmosphere.

14. In an apparatus for drying and conditioning materials, means for circulating a drying atmosphere Within a circulatory path closed to the admission of outside air, means for reheating such atmospere, means for feeding steam t-o the circulatory path for and humidity responsive means for controlling the supply of steam 4upon a ldecrease below a determined limit in tlle moisture content of the drying atmosi ere.y

p 15. In an apparatus f or drying and conditioning materials, means for circulating a Within a circulatory path closed to the admission of outside atmospheric air, means for reheating such atmosphere, temperature controlled means for feeding energy tioning materials, means' for clrculating a to the reheating means,l means for supplylng steam tothe circulan drying atmosphere within a circulatory path closed to the admission of outside atmospheric air, means for reheating such atmosphere, temperature vcontrolled means for feeding energy to the rehcating means, humidlty responsiveA means influenced by an excess humidity in said atmosphere for replacing a definite volume of humid atmos phere with a like volume of fresh atmospheric air, means for feeding steam to said atmosphere during recirculation thereof, and humidity responsive means influenced by a decrease below a determined limit in the moisture content of the atmosphere vfor actuating the. steam feeding means to supply additional moisture to the atmosphere during recirculation thereof.

17. In an appara-tus for drying and conditioning materials, means for recirculating a drying atmosphere Within a`closed circulatory path, a damper-controlled fresh air intake to said path, a damper controlled moist air outlet connected With said circulatory path, means responsive to an excess of the moisture content of the drying atmosphere for vopening the dampers in said fresh air intake and in the moist air outlet for effecting the discharge of a definite volume of moist air from the circulatory path and for feeding to said circulatory path a similar volume of fresh air, means for reheating the air, and temperature .controlled means responsiveto a drop in temperature of the rying atmosphere for feeding energy to the air reheating means.

18. In an apparatus for drying and conditioning materials, means for circulating a drying atmosphere Within a closed'circulatory path, a valved fresh air inlet to said circulatory path, a valved moist air outlet from said circulatory path, means responsive to an excess of humidity in the drying atmosphere for openingsaid moist air outletand said fresh air inlet, means for reheating the drying atmosphere, temperature controlled means for feeding energy to said reheating means, and means responsive to a low humid condition of the drying atmosphere for feeding steam to said atmosphere.

In testimony whereof I have hereto signed my name this 7th day of February, 1924.

' GORDON DoN HARRIS,

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